Computers normally use a cursor which appears on the video screen and moves under the control of a cursor control device. Some cursor control devices are merely keys on the computer keyboard to move the cursor in a horizontal or vertical direction. Key control requires the use of a plurality of keys and is a time consuming method for achieving a desired cursor position.
Cursor positioning has been accomplished with a mechanical joy stick of the type commonly used for video games, and although more rapid control may be achieved in this manner than with key control, joysticks are subject to wear which ultimately results in cursor positioning inaccuracies.
A very popular form of cursor control is the small, hand held "mouse" which is moved by hand over a working surface to provide cursor control signals which cause a controlled movement of a cursor on a display screen. A mouse may be mechanical or optical, but both require a considerable extent of working surface for operation. The mechanical mouse counts the revolutions of a ball or orthogonal wheels which turn as the mouse moves over a surface, while the optical mouse senses a grid to produce cursor command signals.
Alternatively, a number of touch pad control units have been developed in the past. These are generally pressure sensitive or capacitive sensitive touch pads where either the pressure of an operator's finger on a membrane switch array or a change in capacitance resulting from contact by an operator's finger with an array or a single conductive plate provides output control signals for a cursor. These are primarily position sensing units which sense the actual position of a finger or pointer on a touch pad using some type of electronic array which provides a coordinate type of response indicative of position. The output signals from such an array, as illustrated by U.S. Pat. No. 4,550,221 to Mabusth, represent the x and y coordinates of a desired cursor position. A device which provides a velocity control signal by calculating the differences in sensed finger position versus time is disclosed in U.S. Pat. No. 4,988,982 to Rayner.
Pressure sensitive and capacitive or resistive touch pads are subject to wear, friction and the effects of stray electrostatic and electromagnetic fields, and are additionally subject to damage from moisture or liquid spilled on the pad and electronic array. Moreover, the manufacturer may be restricted in choosing a suitable material for the pad surface. In an attempt to circumvent these problems, optical touch entry systems have been developed using opto-matrix light arrays to create a switch matrix and to detect the presence and location of an element in an irradiated field. These systems, as illustrated by U.S. Pat. No. 5,164,714 to Wehner are not subject to wear in high use environments, but they generally require the use of a large surface area, such as a computer screen, bordered by an extensive array of light emitting and detecting elements. The number of light emitting and detecting elements corresponds directly to the number of positions at which the cursor can be positioned in each direction. As such, accurate positioning will not occur without the use of an unacceptably large number of detectors. These systems require large amounts of energy to drive the light emitters and detectors and are often subject to inaccuracy due to ambient light and glare unless complex light modulation systems or ambient light compensation systems are provided.
Of the known, small mechanical cursor positioning devices, the track-ball controller has proven superior as a cursor position controller for portable personal computers and video games. Like other mechanical controllers, however, the track-ball controller has several drawbacks. It can be uncomfortable on the hand, and difficult to use if the ball is small, while a large track-ball controller is difficult to implement on notebook sized personal computers. Finally, being mechanical, it requires maintenance, is subject to wear, and is less reliable than solid state devices.